In a solid state imaging device of rear surface irradiation type which has a wiring layer on a front surface of a silicon substrate and receives light from the rear surface of the silicon substrate, the silicon substrate is typically thinned. Therefore, a red component light (which will be denoted as R light below) having a low absorption coefficient particularly for silicon is not sufficiently absorbed in the thin silicon substrate and transmits through the silicon substrate. Thus, a conventional solid state imaging device of rear surface irradiation type has a poor sensitivity for the R light, which deteriorates a sensitivity of the solid state imaging device.
When the silicon substrate is made sufficiently thick to absorb the R light in order to suppress the deterioration in the sensitivity of the solid state imaging device, a problem such that color mixture occurs is caused. That is, when a blue component light (which will be denoted as B light below) having a high absorption coefficient for silicon is incident into the silicon substrate, most of the B light is absorbed near the rear surface of the silicon substrate and charges are generated. On the other hand, in the solid state imaging device of rear surface irradiation type, a charge accumulating layer is provided at the portion closer to the front surface of the silicon substrate. Therefore, in the conventional solid state imaging device of rear surface irradiation type, when the silicon substrate is made thicker in order to enhance the sensitivity, a distance between a location where charges are mainly generated and the charge accumulating layer is longer and a moving distance of the generated charges is longer. Thus, the generated charges easily move to the charge accumulating layer in an adjacent pixel, and color mixture occurs.
As described above, it is difficult to realize an enhancement in sensitivity and a reduction in color mixture in the conventional solid state imaging device of rear surface irradiation type.